Tool handle switch with overload protection



Nov. 21, 1961 D. w. JOHNSON TOOL HANDLE SWITCH WITH OVERLOAD PROTECTIONFiled Jan. 24, 1958 fl mw M E, wws am Wm 0% Y B United States PatentOfiice 3,009,999 Patented Nov. 21, 1961 This invention relates toelectric switches and more particularly to a. switch useful in thehandles of electric power tools such as saws, drills and the like. Morespecifically, the invention relates to provision in such a switch forautomatic separation of the contacts on the occurrence of apredetermined overload current.

With increasing use of portable power tools in the home andindustrially, a need has arisen for protection of the tool motorsagainst overload. Protection by fuses at a point remote from the toolrequires loss of time in getting at and replacing the fuse. Moreover, anew fuse must be readily available or even greater time is lost. Inportable power tools, there is a considerable tendency among theunskillful persons, and also among both skilled and unskilled whenproceeding with undue. haste, to overload the motor by imposing on thetool a greater load or duty than it was designed to handle normally;

In accomplishing one of the objects of the invention, overloadprotective means, preferably of a kind which can be manually reset, isincorporated in the switch unit itself so that both the switch and itsoverload protective means can be quickly and economically mounted in thetool handle at one time by the tool manufacturer when the tool isassembled.

Another object of the invention is to provide such a switch withmanually resettable overload protection which will trip and remaintripped while the actuator is maintained in the On position. I 7

Another objectis to provide such aswitch in which the overloadprotection is restored or reset to its normaloperating condition byreturn of the: actuator to its Oiff position.

Another object is to provide such a switch with overload protectionincluding a bimetal, inwhich the parts may be returned to normal Onposition and. will remain there only after the bimetal is cooled bydissipation of the heat of the overload. I

Another object of the invention is to provide such a switch withoverload protection, including a bimetallic latch-trip in which it isnecessary not only for the ,bimetal to cool sufliciently to be able toreturn to latching position, but also for the actuatorto be released andreturned to Ofi position before the circuit can again be closed.

Another object is to provide a switch having the foregoingcharacteristics in which the switch actuator or a trigger isautomatically returned to Oil position by a biasing spring which willalso reset the switch and overload means.

Another object is to provide a switch of the foregoing characteristicswhich can be economically manufactured FIG. 2 is a view similar to FIG.1 with the parts in tripped position.

FIG. 3 is a perspective view of the current carrying parts and movablecontact operating slide.

Referring to the drawing, the switch parts are mounted in a body or base10 of molded insulation recessed at appropriate places, as willpresently appear, for reception of the switch parts.

When all the parts are assembled in the base, a fiat liner plate ofsheet insulation (not shown) may be placed over the open face of thebase and held there beneath and by a metal cover plate (not shown) whichis secured on the base in any suitable conventional fashion to mainofthe T lies parallel to one side of the base 10 while the leg 14extendsinto the base and slides in a transverse passage formed near one end ofthe base.

To bias the trigger normally in 011T position of the switch and returnit there automatically when finger pressure on the trigger is released,the leg 14 is formed with a longitudinal groove to receive a coiledcompression spring 16. One end of the spring presses against the end ofthe groove While the other rests against the wall of the base oppositethe passage into which the trigger leg 14 enters.

To operate a movable switch contact, one side of the trigger 14 isprovided with a cam surface 17 which engages the end of a contactoperating slide plate 18 stamped from sheet insulation. This plateslides in a longitudinal slot 19 at right angles to the trigger leg 14.One end of the slide 18 engages the operating cam 17 while the otherengages the movable contact member, designated generally by the numeral20. This movable contact member is stamped from sheet metal in the formof a strip which is laid edgewise in recesses formed for it in the base10'. The movable contact member 20 is U-bent at one end which may becalled the terminal on and is L-shaped at the other or contact end.

The tip 21 of the contact end has a contact button thereon facing andengageable'with a similar button on a normally stationary contact member30, hereinafter more fully described. The tip 21 is joined at a rightangle to a leg 22 extending longitudinally of the base. The'leg 22 is inturn joined to one leg 23 of the two transversely extending legs 23, 25of the U or terminal portion of the member. The legs 23 and 25 arejoined by a connecting portion 24. The connecting portion 24 and the leg25 are both held firmly in their respective recesses in the base whilethe remainder of the member is loosely positioned in its recess so as tobe movable.

and installed in the handles of power tools and the like without theneed for substantial increase in space or major redesign of the handleor substantial increase in the weight of the whole combination.

Other objects and advantages of the invention will ap-- pear as theinvention is described in connection with the accompanying drawing. i i

In the drawing:

FIG. 1 is a plan view of a switch embodying the invention with the coverplate removed and the switch shown in normal Off position andfull linesand in On position in broken lines.

The contact end 21, 22 is biased by inherent springiness of theU-portion 23, 24, 25 into its closed position (dotted in FIG. 1 and fulllines in FIG. 2).

In order to' positively move the movable contact to the normalopen-circuit or Off position, the high point of cam 17 pushes the slide18 to the right (see FIG. 1) when undepressed as in FIG. 1 in fulllines; and the other end of the slide presses against the leg 23 of themovable contact member to separate the contact button from the fixedcontact button on the member 30. On depressing V the trigger, the cam 17moves down or into the base further, during which movementthe slide 18is moved to the left by the spring pressure of the movable contact leg23. This causes the button on the contact tip 21 to engage the contactbutton on the normally stationary contact member E50.

, The two positions as just described are the two normal fOn and Offpositions of the switch.

The normally stationary contact 30 is stamped from sheet metal isinverted L-shape with one end 32 of the L reversely bent and lying in aslot provided for it in the base. The other leg of the contact 30 isflanged along its opposite parallel edges to provide stiffness and has acontact button mounted thereon near its end. The mounting of thereversely bent end 32 in its slot biases the other leg 30 away from themovable contact tip 21.

A slot 18s is .cut into the side of the slide 18 of suflicient widthtopermit passage of the contact end 30 without engagement therewith as theslide moves during normal current operations.

To hold the end 30 fixed in a position where it may be engaged anddisengaged under normal current conditions by the movable contact memberas the trigger is depressed and released, a bimetallic strip 40 isprovided. This also serves on the occurrence of a predeterminedoverload, as a means to release the stationary contact, as willpresently appear. The bimetal 40 extends along the wall of the baseopposite the wall in which the fixed and movable contact members aremounted. Near one end, a slot 42 is cut transversely into one edge ofthe bimetal in position to receive the free end of the stationarycontact member 30. The other end of the bimetallic member opposite thetrigger is bent at right angles and riveted to a substantiallyrectangular terminal-and-rnount ing plate 44 stamped from sheet metal.This terminal plate may be mounted in the base by sliding opposite edgesof the plate in slots running from the open face of the base toward theback wall.

An adjustment bolt 46 passing through the back wall of the base threadsinto an adjustment nut 47 which presses against the bimetal 40 as thebolt is tightened. For this purpose, the recess provided for the nut 46has its wall opposite the bimetal slightly inclined toward the bimetalfrom the open face of the base toward the back of the base, i.e. towardthe bottom of the recess. Thus, the tightening of the bolt and pressureof the nut on the bimetal moves the opposite end of the bimetal slightlyand provides sufficient adjustment for variations in position of thebimetal and for different current settings. A coiled compression spring(not visible) is mounted on the bolt 46 behind the nut, biasing the nutoutwardly of its recess.

In order to reset the bimetal, its free end has an approximately rightangle bend 48 toward the interior of the base. A lip 49 is bent overfrom said bend in position to be engaged by a shoulder 50 formed on theend of the trigger leg 14, as the trigger rises from the ,position ofFIG. 2 to the full line position of FIG. 1.

In order to insure continuous electric contact between the contactmember 3% and the bimetal 40 in all switch positions, a conductive leafspring member 52 of generally L-shape is formed from resilient sheetmetal having a short leg 51 inserted between the two parts of thereverse bend 32 of the fixed contact and a long leg 52 extendingalongside the contact 3t} and slidably engaged at its end with the bend4.8 of the bimetal.

From the foregoing, the operation of the device may be understood. Uponfingerpressure being applied to the trigger 12 when in the position ofPEG. 1, the trigger is depressed against the force of the coilcompression spring 16 This depression allows the slide 18 to move to theleft under the biasing pressure movable contact arm 23 by reason of thehigh point of the cam 17 moving away from the left end of the slide.Thus, the end 21 of the movable contact carries its contact button intoengagement with the button on the normally stationary contact 31, asshown by the dotted lines in FIG. 1.

If the trigger is then released, the spring 16 will return the triggerto its original position. During this return movement of the trigger,the cam 17 moves the slide 18 to the right (as viewed in the drawing),which causes the movable contact to be moved out of engagement with thestationary contact again, thus opening the circuit;

If an overload current had occurred while the trigger was stilldepressed, the heat of the current passing through the bimetal 4% wouldhave caused the bimetal to bend away from the end of the contact 30,releasing the end of that contact from its engagement in the slot 42.Since the contact 30 is biased by its reverse bend 32 that contact willmove to the left and separate from the movable contact as shown in FIG.2. During this movement, as well as' during the normal engaging anddisengaging movement of the movable contact, the leaf spring con nector52 remains at all times in engagement at its lower end with the bend 48of the bimetal and at its upper end in engagement with the reverselybent portion of the fixed contact. This prevents any possibility ofarcing between the lower end of the contact 31 as it is disengaged fromthe slot in the bimetal during circuit interruption on overload.

When finger pressure is removed from the trigger after overloadoperation, the cam 17 pushes the slide 18 to the right. This motion notonly moves the movable contact back to the normal open-circuit positionshown in full lines in FIG. 1, but also forces the normally stationarycontact 3% back to the position of FIG. 1. The movement of the contact30 back to the position of FIG. 1 is accomplished by engagement of oneside of a slot 18s in the slide 18 engaging the leaf spring connector 52and the contact 30. t will be recalled that this slot is wide enough sothat during normal opening and closing movement of the switch, i.e. asthe trigger is depressed and'released during normal current conditions,no side of the slot will engage the contact member 30 or the leaf springconnector 52.

The raising of the trigger after overload also provides for positiveresetting of the bimetal by reason of the engagement of the shoulder 59with the lip 49. However, if the bimetal is still overheated and bent atthe time this resetting movement occurs, and if the trigger isimmediately depressed again, the bimetal lip 49 will follow the shoulder56 during depression of the trigger and will immediately disengage,again, the contact 30 from the slot d2. Thus, the switch cannot bemaintained closed (a) during continuance of an overload condition, or(b) until the bimetal has cooled sufficiently to permit it to againperform its latching and holding function.

For convenience in connecting said wires to the switch parts, springclips or wire gripping members 54 and 55 substantially in the formillustrated in FIG. 3 may be provided. These spring clips, asillustrated, comprise stampings from the resilient sheet metal intoright triangular shape with a gap in the hypotenuse. The clips are eachmounted in recesses provided therefor in the base, the clip 55 beingadjacent the terminal portion 25 of the movable contact member and theclip 54 being adjacent the terminal plate 44 of the bimetal. A pair ofsmall holes or apertures may be formed in the base directly adjacent theterminal plate 44 and terminal 7 portion 25 for the insertion of aconductor wire or wires. As the wires pass through the holes, theyengage the jaws 54 and 55 of the wire gripping members and arefrictionally held by those jaws biting into the wires when any pull isexerted to withdraw the wires. One hole may be used to insert a pin topress the jaw away from the wire when it is desired to release the wire.

An additional gripping member 56 and isolated terminal plate 57 may beprovided for use in making a connection between the cord and motorwinding.

Many modifications within the scope of the invention are possible.Therefore, the invention is not limited to the specific form illustratedand described.

What is claimed is: V

1. An electric switch comprising a depressible operating member biasedin opposition to depression, a member movable by said .operating member,a movable contactmovable by said movable member, another contact towardwhich said movable contact is biased, the bias of said movable contactpressing said movable member toward said depressiblemember, said othercontact being biased to disengage said movable contact, a latchingmember which is normally independent of movement of said depressiblemember and normally holds said other contact latched in a givenposition, said movable contact being movable to engage anddiseugage saidother contact While the latter is thus held, said latching member beingresponsive to overload current to release said other contact, and meansmovable by said depressible member to return said latching member tolatching position, said return means being ineffective to retain saidother contact if the overload conditions are continuing.

2. An electric switch comprising a depressible operating member, amember movable by said operating member, a movable contact movable bysaid movable mernber, another contact toward which said movable contactis biased, the bias of said movable contact pressing said movable membertoward said depressible member, said other contact being biased todisengage said movable contact, a latching member which is normallyindependent of movement of said depressible member and normally holdssaid other contact latched in a given position, said movable contactbeing movable to engage and disengage said other contact while thelatter is thus held, said latching member being responsive to overloadcurrent to release said other, contact, and means movable by saiddepressible member to return said latching member to latching position.

3. An electric switch comprising a depressible operating member, amember movable by said operating member, a movable contact movable bysaid movable member, another contact toward which said movable contactis biased, the bias of said movable contact pressing said movable membertoward said depressible member, said other contact being biased todisengage said movable contact, a latching member which is normallyindependent of movement of said depressible member, and normally holdssaid other contact latched in a given position, said movable contactbeing movable to engage and disengage said other contact while thelatter is thus held, said latching member being responsive ,to overloadcurrent to release said other contact.

4. An electric switch comprising a manually depressible operating memberbiased in opposition to manual operation, a member movable rectilinearlyby said operating member in a direction lateral with respect to movementof the operating member, a movable contact controlled by saiddepressible member, another contact toward which said movable contact isbiased, said other contact being biasedto disengage said movablecontact, a latching member normally holding said other contact in agiven position in which it is engaged and disengaged by movement of saidmovable contact, said latching member being responsive to overloadcurrent to release said other contact, and means movable by saiddepressible member to return said latching member to latching position,i said return-means being inefiective to retain said other contact ifthe overload conditions are continuing.

5. An electric switch comprising a digitallydepress ible operatingmember biased in opposition to digital depression, a member movable bysaid operating member, a movable contact engaged by saidsecond-mentioned member and actuating said movable contact, and anothercontact toward which said movable contact is biased, said other contactbeing biased to disengage said movable contact, and a current-carryinglatching member which is normally independent of-movement of saiddepressible member and normally holds said other con tact latched in agiven position, said movable contact being movable to engage anddisengage said other contact while the latter is thus held, saidlatching member being responsive to overload current to release saidother contact. 6. An electric switch as claimed in claim 5 having meansmovable by said depressible member to return said latching member tolatching position.

7. An electric switch as claimed in claim 5 having means movable by saiddepressible member to return said contact being biased to disengage saidmovable contact,

a current-carrying latching member separate from said other contactnormally engaging and holding said other contact in position to beengaged and disengaged by said movable contact, said latching memberbeing responsive to overload current to release said other contact, andmeans biasing said operating member to a position wherein said contactsare disengaged while said latching member is holding said other contactis position to be engaged by said movable contact.

9. An electric switch comprising an operating member, a movable contactmoving between two positions by operation of said operating member,another contact engageable and disengageable by said movable contact,said other contact being biased to'disengage said movable contact, and acurrent-carrying latching member separate from said other contactnormally engaging and holding said other contact in position to beengaged and disengaged by said movable contact, said latching memberbeing responsive to overload current to release said other contact, andmeans to maintain electrical connection be-. tween said latching memberand said other contact after the latter disengages said movable contact,to avoid arcing between said latching member and other contact.

10, An electric switch comprising an operating member, a movable contactmoving between two positions by operation of said operating member,another contact engageable and disengageable by said movable contact,said other contact being biased to disengage said movable contact, alatching member which is normally independent of movement of saiddepressible member and normally holds said other contact latched in agiven position, said movable contact being movable to engage anddisengage said other contact while the latter is thus held, saidlatching member being responsive to overload current to release saidother contact, an insulating base having slots receiving said contactsfor screwless mounting thereof in said base, and said contacts beingmade of resilient metal strips to impart thereto the aforesaid biasingactions.

11. An electric switch comprising an operating member movable between anoriginal and a second position, an actuating member moved by saidoperating member, a movable contact engageable by said actuating member,another contact engageable and disengageable by said movable contact, alatching member normally holding said other contact in position to beengaged and dis engaged by said movable contact butresponsive tooverload current to release said other contact for separation from saidmovable contact, said actuating member engaging both said contactsduring return of said operating member to original position to restoresaid second contact to said normally-held position and to move saidmovable contact against its bias to second-contact-disengaged position.

I 12. An electric switch as claimed in claim 11 having means'to maintainelectrical connection between said latching member and said othercontact after the latter 7 disengagcs said movable contact, to avoidarcing between said latching member and other contact.

References Cited in the file of this patent UNITED STATES PATENTS2,148,880 Sattler Feb. 28, 1939 2,261,366 Grout Nov. 4, 1941 2,325,650Baxter Aug. 3, 1943 2,357,151 Von Hoorn Aug. 29, 1944 Taylor Jan. 16,1945 OBrien et a1. May 3, 1949 Woodward Dec. 19, 1950 Locher Mar. 31,1953 Euler May 19, 1953 Casey Nov. 17, 1953 Krieger Feb. 8, 1955 Buck eta1. Dec. 18, 1956 Roberts et a1. May 15, 1956

